They’re referring to that one player who can or might tip the scales in favor of one team or the other.

People like Troy Polamalu, the seek-and-destroy Pittsburgh safety. Or Anquan Boldin, the tough-as-nails Arizona receiver, who has taken a backseat to teammate Larry Fitzgerald.

And then there’s a clutch player like Steeler running back Willie Parker who could eclipse them all tonight.

They used to call him “Fast Willie” but this season they’ve been calling him “Wounded Willie.”

A lingering knee injury suffered way back in Week 3 of the regular season has rendered him far less effective than usual. He missed a month of playing time and when he came back he was still less than 100%.

But in two playoff games, Parker has rushed for 193 yards and two touchdowns, giving the Steelers a much-needed running game that helps set up Ben Roethlisberger’s passing game. Now he is back on the big stage where he shone three years ago against Seattle.

In that most recent Pittsburgh Super Bowl win, Parker exploded for a 75-yard TD run and had 93 yards on the ground overall.

“He’s a tough guy,” says Steeler offensive coordinator Bruce Arians. “People think of him as ‘Fast Willie’ an outside runner. He’s a violent little inside runner now. He runs most of the time between the tackles. When he’s back and healthy, he brings such an energy and passion to the game.”

Parker started to feel like his old self in the last weekend of the season when he ran for 113 yards against Cleveland. In the playoffs, he says he has felt better and better with each game. He thinks Pittsburgh’s schedule of games this year, considered to be the toughest schedule of any team in the league, has been good preparation for what lies ahead today.

“We had five-star matchups all year long and we treated every game like it was the biggest game,” he said. “Now, it’s no different – this is the biggest game; it’s the Super Bowl. So we definitely have to go out there and keep the same mentality.”

While trying to keep his jittery nerves in check, Parker can’t deny his excitement at the prospect of what will happen tonight.

“Yes. I can’t lie to you. This game is the biggest of all and even though you know what to expect, the butterflies are going to be there,” he said. “Everybody including your family, your friends, everybody in the NFL, the NBA, the NHL and all the sports are watching. This is the biggest game in the world so yes, of course, you’re going to have butterflies, but after the first kickoff and your first hit, you’ll wake up and get back to it.”

Parker is well aware that Pittsburgh has always been a run-first, grind-it-out ballclub, proud of its blue collar heritage.

“If it’s there for us, if we’re able to move the ball on the ground, we’ll just pound it and pound it and pound it some more. That’s our meat and potatoes. That would be a dream come true for us.”